The present invention relates to a printing system such as a printer or a plotter, particularly to a printing system equipped with a plurality of printer heads suitable for color printing.
Conventionally, a printing system such as a large printer or plotter based on bubble jet printing incorporates a plurality of printer heads for color printing. The plurality of printer heads are arrayed in parallel along the direction in which the carriage moves, and the printer heads incorporate their respective inks, for example, four colored inks consisting of black (Bk), cyan (C), magenta (M), and yellow (Y) inks. The printer heads move together with the carriage, and, while moving, eject, through the nozzles, their respective inks at a specified timing according to given image data, thereby printing an image having the same width with that of the nozzle of one printer head onto a print medium.
Color printing must meet more complicated needs than would be imagined from a cursory look: it deals with the printing of widely varied colored images ranging from simple images primarily composed of lines such as layouts to full-color images such as colored photographs. For example, if an image primarily composed of lines such as a layout must be printed, it is necessary to reproduce the quality of lines, but it is not always necessary to faithfully reproduce the original color of the layout. Indeed, if an image primarily composed of lines is printed, black ink will be preferentially consumed. However, when an image primarily composed of lines is printed, the printed image must be durable (waterproof and weatherproof). Therefore, for such printing, inks prepared from pigments are frequently used. On the other hand, if a full-color image must be printed, it is necessary to reproduce not only the quality of lines but the color of the original image. Therefore, for such full-color printing, utmost efforts have been paid for eliminating unevenness in the printing of color. As one of the means to achieve this, ink used for full-color printing is preferentially prepared from dyes because such ink will allow a comparatively more faithful reproduction of the color of the original image. Accordingly, for a printing system intended to be used for printing full-color images as well as simple graphic images primarily composed of lines, usually a black ink is chosen from inks prepared from pigments, while colored inks (cyan, magenta, yellow) are chosen from inks prepared from dyes.
Ink prepared from pigments, although it is excellent in its water- and weather-proofness, is awkwardly slow to dry. Because of this, if pigment-based and dye-based inks are used simultaneously in printing, a dot printed with pigment-based ink, if put adjacent to a dot printed with dye-based ink, will be blurred. To avoid the blurring of a dot of pigment-based ink printed adjacent to a dot of dye-based ink which would result when the two kinds of dots are printed simultaneously in color printing, the conventional printing system has adopted a method whereby it is possible to print the dots of colored inks in advance of the dots of black ink, instead of printing the two kinds of dots simultaneously. However, this method poses another problem, that is, printing based on this method requires an unduly long time.
This invention was proposed with the above situation as a background, and aims at providing a printing system which will be able to effectively minimize the blurring of ink dots which would otherwise accompany color printing, as well as to reduce the time required for color printing.
To achieve the above object, this invention will provide a printing system comprising: a first black printer head to eject black ink and a plurality of color printer heads to eject colored inks other than black ink both of which are arrayed in parallel along the direction in which a carriage moves; and a second black printer head to eject black ink which is displaced by a certain distance in the direction in which a print medium will be transferred, with respect to the array comprising the first black printer head and the plural color printer heads, whereby it is possible for the second black printer head to print dots such that the dots do not overlap with those printed by the first black printer head or by the plural color printer heads within any given band.
According to this printing system, if an image data for a band concern with a full color image, it is preferable to print the colored image for the band by using the second black printer head and the plural color printer heads. On the other hand, if an image data for a band concern with a black-and-white image, it is preferable to print the black-and-white image for the band by using the first and second black printer heads simultaneously.